A very great many types of folding pocket knives have been developed in which a blade is hinged so as to fold into a handle to cover the sharp blade edge when the knife is being carried and to be unfolded into an extended position for use. In typical folding knives the edge of the blade opposite the sharp edge is slightly exposed and includes a notch or recess for engagement by a fingernail to pull the blade from the stored to the open position.
Such knives may have one or more blades and may have other folding tools such as files, saw blades, scissors, etc. A locking device is often provided to hold the knife in the fully open, use, position and prevent the blade from accidentally folding the sharp blade edge against the user's fingers during use. A button, lever, or similar device may be provided to unlock the blade and allow it to be folded. A similar latch may be provided to releasably hold the blade in the folding position.
Knives, such as those described by Lile in U.S. Pat. No. 4,148,140 and by Sawby in U.S. Pat. No. 4,604,803, have been designed with cylindrical members that have cavities in the exterior of the member or in a sleeve in which the member rotates. A spring loaded ball engages the cavities to releasably hold the knife in an open or closed position corresponding to the cavity location. Non-adjustable coil springs are used. These rotating arrangements are complex and excessively large for a small knife.
Chen describes a knife blade locking arrangement in U.S. Pat. No. 5,875,552 that includes detents in the knife blade with a coil spring and ball arranged in the knife handle to press the ball towards a hole. As the blade is rotated, the ball will be pressed into a blade opening at the open and closed positions. In many cases the small coil spring and ball may not be sufficient to properly hold the blade in the open and closed position. The strength of the small spring is not easily adjustable and the recess for the spring in ball requires a handle of considerably thickness.
A pin mounted on a leaf spring on the exterior of a knife is shown by Jan in U.S. Pat. No. 5,093,995. The pin engages either of two notches in a blade hub to either hold the blade open or closed. To rotate the blade, the pin is pressed until a slot in the pin aligns, whereupon the blade can be pivoted. The exterior leaf spring is likely to catch on clothing when the knife is carried in a pocket or on a sheath, possible bending the spring or tearing the cloth. Further, the pin must be pressed into the knife a precise distance to assure alignment of pin and blade hub.
The knife as disclosed in my earlier U.S. Pat. No. 5,878,500 is eminently suitable for inclusion of the closed blade latch mechanism of this invention. That knife permits easy and rapid one-hand extension to the blade and locking the blade in the extended, use, position.
Thus, there is a continuing need for an improved folding knife that will be automatically latched when closed, that does not require a thick handle or a enlarged blade hub, that includes a closed blade latch that is enclosed entirely within the knife handle and that permits reasonably easy and effective adjustment of blade latching force.